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Control principle
An AFD rectifies AC voltage from line into DC voltage,
after which this DC voltage is converted into an AC
current with a variable amplitude and frequency.
1. Line voltage
3 x 200 - 240 V AC, 50 / 60 Hz
3 x 380 - 460 V AC, 50 / 60 Hz
3 x 525 - 600 V AC, 50 / 60 Hz.
2. Rectifier
A three-phase rectifier bridge that rectifies
AC current into DC current.
3. Intermediate circuit
DC voltage = √2 x line voltage [V].
4. Intermediate circuit coils
Even out the intermediate circuit voltage and reduce
the harmonic current feedback to the line supply.
AEO - Automatic Energy Optimization
Normally, the U/f characteristics have to be set on the
basis of the expected load at different frequencies.
However, knowing the load at a given frequency in
an installation is often a problem. This problem can
be sol-ved by using a VLT 4000 VT with its integral
Automatic Energy Optimization (AEO), which ensures
optimum energy utilization. All VLT 4000 VT units
feature this function as a factory setting, i.e. it is
not necessary to adjust the AFD U/f ratio in order to
obtain maximum energy savings. In other AFDs, the
given load and voltage/frequency ratio (U/f) must be
assessed to carry out correct setting of the AFD.
Using Automatic Energy Optimization (AEO), you
no longer need to calculate or assess the system
characteristics of the installation, since Danfoss VLT
4000 VT units guarantee optimum, load-dependent
energy consumption by the motor at all times.
The figure on the right illustrates the working
range of the AEO function, within which energy
optimization is enabled.
MG.40.A7.22 - VLT is a registered Danfoss trademark
VLT
The motor is thus supplied with variable voltage and
frequency, which enables infinitely variable speed
regulation of three-phased, standard AC motors.
5. Intermediate circuit capacitors
Even out the intermediate circuit voltage.
6. Inverter
Converts DC voltage into variable AC voltage
with a variable frequency.
7. Motor voltage
Variable AC voltage, 10-100% of line supply voltage.
8. Control card
If the AEO function has been selected in parameter
101, Torque characteristics, this function will be
constantly active. If there is a major deviation from the
optimum U/f ratio, the VLT AFD will quickly adjust itself.
Advantages of the AEO function
•
Automatic energy optimization
•
Compensation if an oversize motor is used
•
AEO matches operations to daily or
seasonal fluctuations
•
Energy savings in a constant volume system
•
Compensation in the oversynchronous
working range
•
Reduces acoustic motor noise
®
4000 VT
7
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